The invention relates to a brake booster, in particular, to the construction of a coupling with a master cylinder.
A brake booster includes an enclosed shell, the interior of which is divided by a diaphragm into a plurality of pressure chambers to produce a pressure differential between these pressure chambers, thereby causing a reciprocating movement of a power piston to provide a booster action. To meet the requirement for a reduced weight of vehicle, it is also desired to reduce the weight of the brake booster by reducing the sheet thickness of the shell. However, a reduction in the wall thickness of the shell presents a problem in respect of a reduced strength thereof. A master cylinder is secured to the front side of the shell by means of mounting bolts, which are subject to a tension of an increased magnitude during the operation of the brake booster, presenting a problem relating to the strength of the mounting area.
To accommodate for this, a variety of boosters have been proposed including the provision of a strengthening plate in the region of the mounting bolt in an attempt to improve the strength (see Japanese Utility Model Publication No. 17,402/1985, Japanese Laid-Open Patent Application No. 99,450/1982, etc.).
In the booster disclosed in these examples, the strengthening plate is formed with an opening through which the shank of a mounting bolt extends, and this causes a substantial reduction in the rigidity in the area around the mounting bolt, which has a significant contribution to the strength. The strengthening plate is held between the both head and shell, and this tends to cause a shunt path for a welding current during a welding operation, disadvantageously resulting in a non-uniform welding quality.